Endodontically Treated Tooth

8/13/2019 Endodontically Treated Tooth

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Influence of adhesive techniques onfracture resistance of endodonticallytreated premolars with various residualwall thicknesses

Nicola Scotti, DDS,a RiccardoRota, DDS,b Marco Scansetti, DDS,c

Davide Salvatore Paolino,ING,d Giorgio Chiandussi, ING,eDamiano Pasqualini, DDS,f and Elio Berutti, MD, DDSg

Dental School Lingotto, University of Turin, Turin, Italy; Politecnico diTorino, Turin, Italy

Statement of problem. The choice of restorative method is commonly based on the cavity conguration and the residualnumber of cavity walls. However, the residual wall thickness could be a valuable clinical parameter in the choice of restorationfor endodontically treated teeth.

Purpose.The fracture resistance of endodontically treated premolars was compared with different wall thicknesses restored

with direct composite resin with and without cuspal coverage and with and without

ber post insertion.

Material and methods.This study included 104 intact human maxillary premolars extracted for periodontal or orthodonticreasons. Standardized mesio-occluso-distal cavities were prepared with different palatal wall thicknesses (1.5, 2, and 2.5 mm)and a buccal wall thickness of 2 mm. Teeth were restored with or without a ber post and with or without cuspal coverage.Specimens were subjected to thermocycling (3000 cycles, 5 to 55C) and embedded in polymerized acrylic resin. Teeth weresubmitted to cyclic fatigue followed by a static fatigue test with a universal testing machine; a compressive force was applied30 degrees to the long axis of the teeth until fracture. The results were statistically analyzed by 3-way ANOVA ( a.05).

Results. Residual wall thickness (P.004), the type of adhesive restoration (P


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loss. Of the various post systems avail-

able, metal orber posts are commonly

recommended for clinical use.5 The

introduction of adhesive techniques

and the use of ber-reinforced posts

in conjunction with composite resin

foundation restorations have facilitated

the preservation of tooth structure.6

Moreover, if the post and core havethe same elastic modulus as root

dentin, forces will be distributed along

the long axis of the post, improving the

fracture resistance of endodontically

treated teeth in vitro.7-9 The function of

a ber post is to improve the retention

of the denitive restoration and to

distribute occlusal stressors along the

remaining tooth structure. Posts do

not strengthen endodontically treated

teeth,10,11 especially anterior teeth,12

although some studies have suggested

that cast metal posts result in reduced

stresses in the dentin.13

However, endodontically treated

teeth restored with direct techniques,

with or without posts, may sometimes

present residual compromised cusps

that could eventually fracture. In these

patients, reduction and coverage with a

complete crown is usually indicated to

prevent coronal fracture.14,15 However,

the concept of minimal intervention

dentistry to maximize preservation of the

tooth structure is gaining popularity in

the restoration of endodontically treated

teeth.13 Tooth structure preservation is

directly correlated with fracture resis-

tance,16,17 reducing the occurrence of

catastrophic failures and enhancing the

longevity of the restoration. In vivo and

in vitro studies support the use of

direct intracuspal adhesive techniques

for the restoration of endodonticallytreated teeth if a normal occlusion

without parafunction is present.18,19

This approach has the advantage of

reinforcing teeth without occlusal

coverage.20-22 To date, few prospective

clinical studies have evaluated the

different types of direct or indirect ad-

hesive restorations of endodontically

treated teeth. Mannocci et al23 found

ber posts and direct composite resin

restorations to be more effective thanamalgam in preventing root fractures,

but not secondary caries, of endodonti-

cally treated premolars. Another pro-

spective in vivo study24 showed similar

3-year survival rates between endodon-

tically treated premolars restored with

ber posts and direct composite resin

restorations and complete coverage with

metal ceramic crowns.

The thickness of the residual cavitywall could be a simple but effective

parameter for clinically evaluating the

remaining tooth structure and conse-

quently for the selection of the most

appropriate type of restoration for

endodontically treated teeth. However,

this parameter has not been investi-

gated extensively. The choice of restor-

ative method is commonly based on the

cavity conguration and the residual

number of cavity walls.25,26 However,

because the residual cavity wall thick-

ness represents the quantity of remain-

ing enamel and dentin and is directly

correlated with the residual sound tis-

sue,27 wall thickness evaluation could

provide more information to the clini-

cian regarding the fatigue resistance

of an endodontically treated tooth.

Therefore, the purpose of this in vitro

study was to evaluate the effect of

cavity wall thickness on the fracture

resistance of endodontically treated

teeth restored with a variety of adhesive

techniques. The null hypothesis tested

was that residual wall thickness does

not inuence the fracture resistance

or fracture mode of endodontically

treated premolars restored with or

withoutber posts and with or without

cusp coverage.

MATERIAL AND METHODS

After receipt of institutional board

approval, the study included 104 non-

carious single-rooted maxillary pre-

molars with mature apices recently

extracted for orthodontic or peri-

odontal reasons. The inclusion criteria

were an absence of restorations, similar

crown and root sizes, and no cracks

under transillumination. Selected teeth

were stored in 0.5% chloramine T tri-

hydrate at 4

C. After cleaning the toothsurfaces, endodontic treatment was

performed on all specimens except

those in the control group (intact teeth;

n8). Specimens were endodontically

instrumented with Pathles (1-2-3) and

ProTaper (S1-S2-F1-F2-F3) (Dentsply

Maillefer) to the working length,

enlarging the apex to a size 30, 0.09

taper. The specimens were irrigated

with 5% NaOCl alternated with 10%EDTA (ethylenediaminetetraacetic acid)

with a 2-mL syringe and 25-gauge

needle. Specimens were obturated

with gutta percha by using a heat

source (DownPack; Hu-Friedy) and an

endodontic sealer (Pulp Canal Sealer

EWT; Kerr Corp). Backlling was per-

formed with the Obtura III system

(Analytic Technologies).

After 24 hours, all specimens were

assigned to 3 groups (W1.5; W2; W2.5;

32 teeth each) based on the thickness

of the residual palatal wall (1.5, 2, and

2.5 mm) after cavity preparation,

measured with a caliber at the occlusal

oor of the cavity. The specimens were

treated as reported by Scotti et al.22 In

each tooth, a class II mesio-occluso-

distal cavity was prepared. In order to

compensate for different coronal anat-

omy, all teeth were prepared by hand by

1 experienced operator. The prepara-

tion was extended until the gingival

cavosurface margin was 1-mm coronal

to the cement-enamel junction. The

residual thickness of the buccal cusps at

the height of the contour was 2 0.2

mm. Within each group, the specimens

were further randomly assigned to 4

subgroups (8 teeth each) on the basis

of the restoration type (Table I). In the

groups with cusp coverage (overlay),

both cusps were reduced with a

completelyat enamel margin of up to2 mm.

In the ber post groups, the post

space was prepared with drills from the

post manufacturer (Dentsply Maillefer)

to a depth of 7 mm, measured from the

pulpal chamber oor. All adhesive

procedures were performed with All-

Bond 3 (Bisco) according to the man-

ufacturers instructions. For ber

post cementation, a dual-polymerizing

cement (NanoCore Dual; Dentalica)was used. Dual-polymerizing cement

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was applied into the canal by using a

tube with a needle and the appropriate

plug (KerrHawe SA) and by injecting

the materials into the post spaces with

a specic Composite-Gun (KerrHawe

SA). Size 1 RTD ber posts (RTD) were

cemented to the full depth in the

prepared post spaces. After initial

preparation, photopolymerization wasperformed with an LED-polymerization

light for 40 seconds (Translux; Heraeus

Kulzer) at 1200 mW/cm2.

After xing the matrix band with a

retainer, A2-shaded nanohybrid com-

posite resin (Venus Diamond; Heraeus

Kulzer) was placed by using an oblique

layering technique. Each layer, 1.5 to

2 mm thick, was polymerized for 20

seconds with an LED-polymerization

lamp at 1200 mW/cm

2

(Translux Po-wer Blue; Heraeus Kulzer). The matrix

band and retainer were then removed,

and postpolymerization was performed

on the buccal and lingual aspects of the

boxes for 40 seconds on each side. All

the restored specimens were nished,

polished, and then stored in distilled

water at 37C for 7 days. All specimens

were subjected to 3000 thermal cycles

between 5 and 55

C for 60 secondseach. All specimens were embedded in

light-polymerizing acrylic resin to 1 mm

below the cement-enamel junction,

with a thin layer of polyvinyl siloxane

(Aquasil; Dentsply Italia) around the

root to simulate the periodontal liga-

ment. Specimens were then exposed to

cyclic loading (Mini Bionics II; MTS

Systems) with an inclination angle of 30

degrees to the long axis of the tooth

and at a frequency of 8 Hz, startingwith a load of 20 N for 5000 cycles,

followed by a stage of 50 N for 20 000

cycles. A 10-mm-diameter metal ball

was used. The site of loading was the

central ssure of the occlusal surface of

the restoration in the direction of the

buccal cusp. The specimens were then

submitted to the static fracture resis-

tance test by using a universal testing

machine (Instron) with a 2-mm-diam-eter steel sphere crosshead welded to

a tapered shaft and applied to the

specimens at a constant speed of

2 mm/min and at an angle of 30 de-

grees to the long axis of the tooth. The

forces necessary to fracture each tooth

were measured in newtons (N).

Restorable and nonrestorable frac-

tures were distinguished by using an

optical stereomicroscope with agree-

ment by 2 examiners. Restorable fail-ures included fractures above the

Table I. Specimen characteristics, grouping, mean fracture resistance values (Newtons), and fracture modes ofvarious groups

Group

(n[32)

Residual Wall

Thickness

Subgroup

(N[8) Characteristics

Fracture

Resistance

(mean SD)

Nonrestorable

Fracture (%)

W1.5 1.5 mm W1.5 A Post (-), cuspcoverage (-)

260.51 82.69 87.5

W1.5 B Post (), cuspcoverage (-)

445.71 103.19 62.5

W1.5 C Post (-), cuspcoverage ()

793.11 196.56 87.5

W1.5 D Post (), cuspcoverage ()

775.98 173.30 87.5

W2 2 mm W2 A Post (-), cuspcoverage (-)

313.77 69.61 75

W2 B Post (), cuspcoverage (-)

660.59 149.48 50

W2 C Post (-), cusp

coverage ()

801.16 175.28 87.5

W2 D Post (), cuspcoverage ()

868.58 139.76 87.5

W2.5 2.5 mm W2.5 A Post (-), cuspcoverage (-)

368.22 130.27 87.5

W2.5 B Post (), cuspcoverage (-)

676.06 155.56 50

W2.5 C Post (-), cuspcoverage ()

821.18 121.45 75

W2.5 D Post (), cuspcoverage ()

871.77 150.74 87.5

Control(n8)

- - Intact teeth 1098.64 287.86 20

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cement-enamel junction, meaning that

the tooth could be restored even in in-

dividuals with major coronal tissue loss.

Nonrestorable failures included fracture

patterns that extended below the

cement-enamel junction, in which a

surgical approach would be required to

perform an adhesive restoration.

A statistical analysis of variance(3-way ANOVA, including 2-way and

3-way interactions, a.05) was per-

formed to evaluate the inuence of the

residual wall thickness (factor T at

levels 1.5, 2, and 2.5 mm), the resto-

ration (factor R at inlay and onlay

levels), and the ber post (factor P at 2

levels) on the fracture resistance of the

tooth. A c2 test was used to compare

the failure modes of the specimens.

Differences were considered statistically

signicant at values ofa.05.

RESULTS

The mean fracture resistance values

and the modes of failure observed in

the groups are listed in Table I. The

normal probability plot showed that

the residuals followed a normal distri-

bution. None of the tested restorations

showed similar fracture resistance

values to the control group, even

those with residual walls of 2.5 mm.

Within the restored specimens, ANOVA

(Table II) showed that the thickness of

the residual wall (P.004), the type of

adhesive restoration (P


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treated premolars. Regardless of wall

thickness and post placement, teeth

with cusp cupping (factor restoration

at level onlay) showed the greatest

fracture resistance.

The c2 test showed statistically sig-

nicant differences in the patterns

of fractures between the subgroups

(c2

18.133; P


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undergoing root canal treat-

ment.10,13,27,39 According to Aquilino

and Caplan,13 although ceramic or

composite resin onlays could protect

against fractures, no reports support

their use in the restoration of posterior

teeth. Some in vitro studies concluded

that endodontically treated teeth

recovered the lost resistance to fractureafter receiving an indirect restoration

with cusp protection.22 The tendency of

onlay composite resin restorations to

receive higher load might be attributed

to the dispersion of compressive

stresses. Similar results were found for

cusp coverage with amalgam,39 which

signicantly increased the fracture

resistance of the teeth compared to

those restored without cusp coverage.

In contrast to the study by Soares

et al,40 cuspal reduction restorations

reduced fracture resistance in mandib-

ular premolars, probably because of the

large amount of sound tooth tissue

removed during specimen preparation.

Other authors have stated that cusp

coverage does not strengthen premolars

restored with composite resin onlay32

or molars with ceramic restorations.41

This may be due either to the different

axial direction of the compressive load

used in these studies, or to the different

indirect restoration, which involved

only a buccal cusp. Moreover, in this

study, the insertion of a ber post

within the cuspal coverage restoration

did not signicantly increase fracture

resistance, probably as a result of the

adequate dispersion of compressive

stresses already provided by the com-

posite resin overlay.21,26,30

Regarding failure mode, the combi-

nation of the ber post with an inlayadhesive restoration led to a higher

incidence of more favorable failure

types (P2 mm, less

invasive treatments such as direct in-

tracuspal composite resin restoration

supported by ber-post insertion can

provide sufcient fracture resistance to

occlusal loads. In contrast, when the

residual wall thickness is


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Corresponding author:

Dr Nicola Scotti

Via Nizza 230, 10100 Turin

ITALY

E-mail:[email protected]

Copyright 2013 by the Editorial Council for

The Journal of Prosthetic Dentistry.

82 Volume 110 Issue 5

The Journal of Prosthetic Dentistry Scotti et al
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